Not tonight honey, my hair is growing

A medication for male pattern baldness may cause sexual dysfunction in men, even long after they stop taking the drug, according to this Time report on a new study. The hair-loss drug finasteride, marketed as Propecia and Proscar by Merck, may cause low libido and impotency.

Here’s more from the story:

Participants had taken finasteride for 28 months on average, and reported sexual problems for an average 40 months, but the study author said that 10% of the surveyed men had used the drug for less than a month.

The medication carries a warning about persistent sexual dysfunction, along with potential psychological problems, in the U.K. and Sweden. But U.S. labeling doesn’t contain such warnings.

Doctors have long known that finasteride can cause impotence and related sexual problems. Finasteride decreases the conversion of testosterone to the more potent dihydrotestosterone, the latter of which is related to hair loss. Yet any medication that interferes with testosterone runs the risk of also affecting sexual performance.

In fact, GlaxoSmithKline and Merck, who both sell finasteride for several medical conditions, have reported that up to 8 percent of users have adverse sexual events. A review study published in 2008 in the Journal of Sexual Medicine extends that range to 38 percent, depending on dose and duration.